In recent years, semiconductor lasers have been used in various fields, such as house hold electrical products, office automation equipment, communication devices and industrial measuring instruments. Efforts are focused on developing short wavelength semiconductor lasers, among semiconductor lasers, for the purpose of applying them to high density optical disk recording, laser display and the like expected to be used in many fields.
In particular, regarding GaN-based semiconductor lasers, the wavelength can be shortened up to 350 nm or less, and the laser oscillation operation in 400 nm is reported. In terms of reliability of the material, a reliability for 10,000 hours or more of a light emitting diode (LED) is confirmed. The GaN-based semiconductor lasers have possibilities of oscillation in a wide wavelength range, and therefore are preferable for the application to laser displays and the like.
However, in consideration of the application to laser displays and the like, high power is required for driving. For this reason, it is desirable in view of power consumption to obtain semiconductor lasers with low operation voltage. In self standing semiconductor lasers, for example, an interface between the back surface of the GaN substrate and an electrode is mentioned as a portion having a high resistance. Such a high resistance portion makes it difficult to reduce the operation voltage.
There is proposed a technique to process the back surface of the substrate of a GaN-based semiconductor laser to be in an irregular shape to achieve an electrode with low contact resistance. There is also proposed a semiconductor laser in which cleavage assistant grooves are provided in a sapphire substrate to improve the cleavage property.